I measured the signal generator alone, not connected to the input. It goes to 4.5V high and 0.001V low. Then I connected it to the input and measured at the input. I got 4.5V high and 1.1V low.
Also I ordered the 74LVC1G07 buffer along with a breakout board which should allow me to hook it up inline and test. I'll report back when I do.